var log = console.log;
var user = {
    username: "zhangsan",
    age: 20,
    sex: "male"
};
log("username:%s", user.username); //拿后面的变量替代前面的占位符
log('age:%d', user.age);
log('user:%j', user);
log(`${user.username}`); //模板字符串，反引号``引出